The invention relates to a method of replenishing and/or providing water-displacing treating liquids or mixtures of these treating liquids and of water-absorbing liquids in treating compartments, which liquids are used to remove water from the surfaces of objects to be immersed in the treating liquids, said objects being made of glass, ceramic, nickel, copper, stainless steel or synthetic resin such as, for example, disc-shaped information carriers.
In the art there is a need for methods of removing liquids from objects whose surfaces are contaminated by said liquids. In the case of, for example, optically-readable disc-shaped information carriers such as, compact-discs the water used to clean them must be removed after the cleaning process. The same applies to silicon discs and copper and glass components which are used in electric circuits. When such objects are dried it is important that no deposition residues are left behind on their surfaces in the form of drying spots. Moreover, to avoid mechanical attack of the objects to be dried, it is to be noted that in the drying process certain predetermined temperatures are not to be exceeded. When drying, for example, disc-shaped information carriers such as, for example, compact discs, a temperature of 90.degree. C. must not be exceeded. A further important factor in drying is that the objects to be dried are not contaminated by particles which are suspended in the treating liquid. Consequently, high-grade, i.e. highly pure, treating liquids must be used.
DE-OS No. 23 01 357 describes a method and an arrangement for removing liquids from solid surfaces, according to which method an object having a surface which is contaminated by a liquid is immersed in a solvent-containing bath, the density of the solvent being different from that of the liquid. The solvent is agitated, thereby removing the liquid from the object. The liquid and the solvent are discharged from the bath and after the solvent has been separated from the liquid it is fed back to the solvent-containing bath. This method requires a very pure solvent which is very expensive. Moreover, when high demands are imposed upon the purity of the solvent it must be refreshed very frequently, thereby rendering uneconomical this method of removing liquids.
DE-OS No. 31 25 980 describes a method of manufacturing carriers having a high information density, in which surface impurities are first removed by an aqueous rinsing agent which is subsequently removed by rinsing the carriers with a liquid fluorocarbon. Next, the carrier is maintained in a fluorocarbon vapour until the carrier temperature equals the vapour temperature. Also in this method the liquid fluorocarbon must be very pure, and as it is contaminated in the disc-rinsing process it must be frequently refreshed.
It is an object of the invention to provide a method of replenishing and/or providing water-displacing or water-absorbing treating liquids, which allows for an efficient use of solvents so that the preparing and replenishing of absolutely pure treating liquids can be dispensed with.
This object is achieved according to the invention, by a method in which the surfaces of the treating liquids in the compartments are kept at such a temperature that a similar, vaporized treating liquid which is provided over these surfaces condenses on those surfaces.
Such a method of replenishing and/or providing water-displacing or water-absorbing treating liquids or mixtures thereof has the advantage that the treating liquids present in the liquid phase in treating compartments can be replenished continuously with a similar liquid which is provided in the vapor phase and which condenses on the surfaces of the liquid phase treating liquids in the treating compartments.
As the treating liquids are first vaporized and are not used as a treating liquid until they have condensed, an inevitable purification of the treating liquids takes place because due to the vaporization they cannot entrain the solid contaminations. This is advantageous, both in filling the treating compartments, i.e. when they are filled for the first time, and in the continuous regeneration of the liquids in the treating compartments. In order to continuously regenerate the treating liquids in the treating compartments, these liquids are discharged from the treating compartments, vaporized and condensed again on the surfaces of the liquid in these compartments. In this way the treating liquids are continuously subjected to a process in which they are vaporized and, thus, purified and cleared of water. Thus, this method is economically feasible and, moreover, provides a highly pure treating liquid.
This method can be applied to water-displacing treating liquids, mixtures thereof and water-absorbing liquids.
The selection of the temperatures of the treating liquids in the treating compartments depends on the composition of these liquids and on the material and properties of the objects to be treated. In any case, the temperature of the treating liquids in the compartments must be kept below the vaporization temperature of the liquids if a vaporized similar treating liquid which is situated above the surfaces of the treating liquids is to condense on these surfaces.
In accordance with a further embodiment of the inventive method, the vaporous treating liquid which condenses on these surfaces is vaporized by heating in a vaporization compartment.
In a vaporization compartment the treating liquids can readily be vaporized by heating. Consequently, both treating liquids which are discharged from the treating compartments and fresh, unused treating liquids can be supplied to said vaporization compartment. The vaporization compartment must be arranged so that the vaporized treating liquid is supplied to the surfaces of the treating liquids in the treating compartments where the vapour will then condense.
According to a further embodiment of the inventive method, a mixture of a fluorocarbon and an alcohol is used as a treating liquid. An exmple of a suitable fluorocarbon is 1,1,2-trichloro-1,1,2-trifluoro-ethane.
If water is to be removed from the surfaces of the objects to be treated, a liquid fluorocarbon is a suitable treating liquid because its specific gravity is higher than that of water and it removes the water from the surfaces of the objects to be treated. When the alcohol is added to the fluorocarbon, the removal of moisture from the surfaces of the objects to be treated is facilitated because alcohol absorbs water. Suitable alcohols are, for example, isopropanol, methanol, ethanol and butanol.
According to a further embodiment of the method of the invention, the mixture of the fluorocarbon and alcohol in the treating compartments is kept at a temperature which is from 7.degree. C. to 15.degree. C. below the boiling point of the mixture.
Advantageously, this temperature range is observed because on the one hand the temperature of the water in the ambient air does not fall below the dew point, and thus the formation of a water film on the liquid mixture in the treating compartments is avoided, and on the other the temperature is seleted so that the vaporized treating liquid above the compartments condenses on the fluid treating liquids in the compartments. Moreover, in order to ensure an adequate replacement of the treating liquid in the compartments, the temperature of the treating liquids in the treating compartments must be selected so that a sufficient quantity of the vaporized treating liquid condenses on the surfaces.
According to a further embodiment of the invention, the alcohol concentration of the liquid fluorocarbon-alcohol mixture in the vaporization compartment, which mixture is to be vaporized by applying heat, is such that the vaporous treating liquids and the treating liquids which are in the treating compartments are azeotropic or of a similar composition. In order to ensure that the mixture in the treating compartments is azeotropic, the alcohol concentration in the vaporization compartment must at least be sufficient so that the mixture is azeotropic. An upper limit is set to the alcohol concentration in the vaporization compartment by the fact that the fluorocarbon-alcohol mixture should be free of inflammable vapors. Thus, the alcohol concentration generally lies between 1.5 and 15% by weight.
According to a further embodiment of the invention, water and/or water-contaminated treating liquid are/is led from the surfaces of the treating liquid in the treating compartments to at least one water separator by means of overflow devices, after which they/it are/is supplied to a storage tank, from where they/it are/is pumped through a filter and vaporized in the vaporization compartment.
As the water or the water-contaminated treating liquid has a lower specific gravity than the uncontaminated treating liquid, the water or the water-contaminated treating liquid accumulates at the surface of the liquids in the treating compartments. Subsequently, overflow devices supply the water to a known water separator which operates according to the principle of gravity. The treating liquid is then led into a storage tank which is designed so that the treating liquid used in the process does not have to be replaced continuously but rather at irregular intervals. From the storage tank the treating liquid is pumped through a filter in which it is purified mechanically. After filtering the liquid flows into an arrangement in which it is vaporized again.
According to a further embodiment of the invention, the vaporized treating liquid is also used for rinsing the condensate off an object which is pulled out of a treating liquid in treating compartment.
As the temperature of the fluid treating liquid in the treating compartments is below the vaporization temperature, the vaporized treating liquid can also be used for rinsing a condensate. If an object is pulled out of the treating liquid in the treating compartment after it has been immersed therein for a sufficiently long time, its temperature will be substantially equal to that of the fluid treating liquid, i.e. a temperature below the vaporization temperature. Consequently, after the object has been pulled out the vaporized treating liquid will deposit as a condensate on the surface of the object and rinse it. Thus, the vaporous treating liquid is used twice, namely on the one hand to replenish the liquids in the treating compartments and on the other to rinse the condensate off the objects which are pulled out of the liquids in the compartments.
According to a further embodiment of the invention, the vaporized treating liquid is contained in a bounded space in the upper part of which there is a cold trap from where the condensed, water-contaminated treating liquid is led to a water separator and subsequently passed on to a treating compartment.
The space above the treating compartment, in which vaporized treating liquids are present, is essentially closed, although it must have an aperture to enable objects to be supplied to or withdrawn from said space. To separate said aperture from the vapour present in the space, a cold trap is provided in the vicinity of the aperture, on which both the vapour of the treating liquid and the water vapour condense. The treating liquid is separated from the condensed water in a water separator. The treating liquid is then again supplied directly to the treating compartments or to the storage compartment.
According to a further embodiment of the inventive method, the treating liquid is cooled in the water separator(s), thereby obtaining the desired temperatures of the treating liquids in the treating compartments. The cooling of the treating liquids has the additional advantage that the water can be separated more readily.
An exemplary embodiment of the invention will now be explained in more detail with reference to the drawings, in which